Animal-Assisted Intervention programs and interventions with students are becoming promising field in school and therapeutic settings. Following this trend, Animal-Assisted Intervention (AAI) program was designed to help students adopt more easily to school life and to encourage them to keep healthy relationships with others. Accordingly, the purpose of this study was to identify the effects of animal-assisted intervention (AAI) on the middle school students' sociability and depression. The participants in this study, 8 middle school students residing in Seoul who were interested in animals and agreed to the research attended this program. This study was conducted two times a week for 6 weeks (a total of 12 times) with one main researcher and three research assistants. The major research tool was the test of sociability and depression and the statistical test being used for this study was Wilcoxon's signed ranks. The results were as follows. First, the study showed the significant effects of animal-assisted intervention on sociability for middle school students. There were significant differences in many aspects such as reliability, autonomy, sociability and compliance. Second, significant reductions in anxiety and depression were found after the introduction of animal-assisted intervention for students. Students who participated this program experienced a reduction in depression and stress to some degree. Also, they began to form much more positive friendships and followed school rules as well. Based on the above results, it can be seen that animal-assisted intervention program significantly has the positive effects on the social adaptability and depression of the middle school students. Therefore, this animal-assisted intervention should be considered as a positive program for emotional and psychological support for middle school students.